Hydrogen in Steels

Hydrogen in Steels  Hydrogen (H) (atomic number 1 and atomic weight 1.008) is a colourless gas. It has a density of 0.0899 gm/litre. Melting point of H is – 259.2 deg C and boiling point is -252.8 deg C. The phase diagram of the Fe-H  is given at Fig 1. Fig 1 Fe-H phase diagram  H in steels is considered as an undesirable impurity which is quite harmful in certain applications. It is always a source of various problems within steel production because of its generally detrimental effects on processing characteristics and service performance of steel products. Just a few parts per million of H dissolved in steel is sufficient to do the harm. Hence where necessary, it should be avoided or removed as required. Source of hydrogen There are multiple sources identified for H to enter into steel by any of several routes. In the primary steel making furnace, source of H is water which enter the furnace through wet scrap, flux materials, ferro alloys and refractory materials which are not fully dried. Water dissociates on contact with liquid steel and produces H which is absorbed by the steel bath. This H generally get removed by the purging action of the carbon (C) boil, but some can remain in the steel. Contact between the liquid steel and moisture in refractory materials  of the steel teeming ladles and/or humid air can cause pick up of H by the liquid steel. The hydrophilic calcium oxide (CaO) in the slag and decomposition of refractory binders which are required for sufficient thermal shock resistance, also account for H entering into the steel. Dissociation of water vapour (equation given below) contained in furnace gases generated during the steel making practices employing the combustion of hydrocarbon fuels produces H...

Industrial gases used in steel industry...

Industrial gases used in steel industry The term “Industrial gas” refers to a group of gases (Fig 1) which are specifically produced for use in a variety of industrial processes. They are distinct from the fuel gases. Speciality gases such as neon, krypton, xenon and helium are sometimes considered under the category of industrial gases.  Industrial gases are produced and supplied in both gas and liquid form and transported in cylinder, as bulk liquid or in pipelines as gas. Industrial gases usually used in steel industry are oxygen, nitrogen, argon and hydrogen. Fig 1 Industrial gases Oxygen Oxygen (O2) is an active component of the atmosphere making up 20.94 % by volume or 23 % by weight of the air. It is colorless, odorless and tasteless. Oxygen is highly oxidizing.  Oxygen reacts vigorously with combustible materials, especially in its pure state, releasing heat in the reaction process. Many reactions require the presence of water or are accelerated by a catalyst. Oxygen has a low boiling/ condensing point which is -183 deg C. The gas is approximately 1.1 times heavier than air and is slightly soluble in water and alcohol.  Below its boiling point, oxygen is a pale blue liquid slightly heavier than water. Properties of oxygen are at Tab 1. Oxygen is produced in large quantities and at high purity as a gas or liquid by cryogenic distillation and in smaller quantities as a lower purity gas (typically about 93%) by adsorption technologies such as pressure swing adsorption (PSA) or vacuum pressure swing adsorption (VPSA or VSA). Oxygen is the second largest consumed industrial gas.  Aside from its chemical name O2 oxygen is also referred to as GOX or GO when produced and delivered in gaseous form, or as LOX or LO when in its cryogenic liquid form. Oxygen is...